Chronic ingestion of alcohol can affect many aspects of hematopoiesis and the function of hematopoietic lineage cells. The deleterious effects of chronic alcohol include thrombocytopenia, neutropenia and lymphopenia, as well as pancytopenia. Vacuolization of bone marrow cells is common and, although rare, hypocellularity of the bone marrow has been observed. Many patients show a marked immunodeficiency associated with neutropenia and lymphopenia. The hematological complications observed in alcoholic patients suggest that alcohol abuse places excessive demands on the hematopoietic system. Throughout life, the hematopoietic system is maintained by a population of self-renewing, pluripotent hematopoietic stem cells (HSC's) that generate all of the hematopoietic lineages through the production of oligopotent progenitors. HSCs are rare in the bone marrow yet, due to their self-renewal, they are long-lived and under normal circumstances are not depleted within the lifetime of the organism. However, there are studies that suggest that HSCs can be exhausted under extraordinary circumstances. The hypothesis to be tested in this proposal is that alcohol abuse imparts excessive demands on the hematopoietic system that can lead to premature senescence of HSC's. Corollary hypotheses that will also be addressed are that alcohol has a direct toxic effect on HSC's; and alcohol adversely affects the microenvironment of the bone marrow leading to aberrant hematopoiesis. The goals of this proposal are to determine the effects of chronic alcohol ingestion on the number, longevity, and function of HSCs using a murine model. The effects of alcohol on the different stages of hematopoietic development will be determined at the phenotypic and functional levels and the effects on the microenvironment will be assessed by determining the effects of on the expression of hematopoietic cytokines and the ability of the marrow to sustain hematopoiesis. The effects of alcohol on the in vivo function of HSC's will be determined by competitive reconstitution assays at limiting dilution. To determine if alcohol accelerates senescence of HSC's secondary and tertiary transplantations of HSC's will be done over a three-year period. To determine whether normally quiescent HSC's are activated by alcohol feeding, the sensitivity of these cells to cytotoxic drugs will be assessed by quantitating surviving HSC's and determining the rate of recovery of bone marrow homeostasis following injection of the cytotoxic drug. [unreadable] [unreadable] [unreadable]